1. Field of the Invention
The invention relates to a compact, reliable, high performance, strip line filter, and to a duplexer filter including such a strip line filter.
2. Description of Related Art
Simply constructed and compact, high performance dielectric filters are known for use in mobile telecommunication systems, such as portable telephone systems which operate in the microwave frequency band. Such a known dielectric filter is formed with a unitary, rectangular box-shaped dielectric block which is provided with conductive electrodes, for example metal plating that covers the front, back, bottom and left and right side faces. A row of cylindrical holes passes through the body of the dielectric block, from the bottom face to the top face. Cylindrical inner conductors, forming dielectric resonators, are arranged on the walls of the holes. On the top face, conductive resonance frequency adjusting electrodes are laid out in parallel spaced relation, so as to surround and be connected to the upper ends of the respective inner conductors. The metal plating on the bottom face surrounds, and is connected to, the lower ends of the inner conductors. Input and output pins, surrounded by insulating discs at their upper ends, are inserted into the end holes at opposite ends of the row, for connecting the filter to an external circuit.
The dimensions of the above-described conventional dielectric filter are critical to the quality factor Q of the resonators, and thus the performance of the filter. Therefore, if the width of the filter is reduced as part of an effort to produce a more compact telecommunication apparatus, the Q of the resonators is reduced.